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Re: [PATCH v4 03/12] target/arm: Fix mte_checkN

From: Alex Bennée
Subject: Re: [PATCH v4 03/12] target/arm: Fix mte_checkN
Date: Thu, 08 Apr 2021 11:02:57 +0100
User-agent: mu4e 1.5.11; emacs 28.0.50

Peter Maydell <peter.maydell@linaro.org> writes:

> On Wed, 7 Apr 2021 at 19:54, Alex Bennée <alex.bennee@linaro.org> wrote:
>> Richard Henderson <richard.henderson@linaro.org> writes:
>> > We were incorrectly assuming that only the first byte of an MTE access
>> > is checked against the tags.  But per the ARM, unaligned accesses are
>> > pre-decomposed into single-byte accesses.  So by the time we reach the
>> > actual MTE check in the ARM pseudocode, all accesses are aligned.
>> >
>> > Therefore, the first failure is always either the first byte of the
>> > access, or the first byte of the granule.
>> >
>> > In addition, some of the arithmetic is off for last-first -> count.
>> > This does not become directly visible until a later patch that passes
>> > single bytes into this function, so ptr == ptr_last.
>> >
>> > Buglink: https://bugs.launchpad.net/bugs/1921948
>> Minor note: you can Cc: Bug 1921948 <1921948@bugs.launchpad.net> to
>> automatically copy patches to the appropriate bugs which is useful if
>> you don't have the Cc for the reporter.
> I'm not sure cc'ing bugs on patches is very useful, though (and especially
> not for big series). I usually prefer to just add a note to the bug with
> the URL of the series in patchew afterwards.

Ideally the tooling would pick up bug links in Patchew and automatically
update the relevant bugs when new series are posted. I only mentioned it
because the original bug reporters weren't Cc'ed on the patches and lo
now they know about the iteration they have tested it ;-)

Alex Bennée

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